Many types of electrical and electronic based systems may use rechargeable multi-cell batteries. These systems can include, for example, renewable energy systems, electric vehicles, hybrid electric vehicles, and commercial electronics. Many battery cell technologies (e.g., lead-acid, nickel-cadmium (NiCd), nickel metal hydride (NiMH), lithium-ion, Lithium Iron Phosphate (LiFePO4) and nano Lithium Titanate Oxide (nLTO)) can provide the energy storage needed for the systems.
Several design deficiencies in currently available fixed configuration rechargeable multi-cell battery systems have impeded the use of rechargeable multi-cell batteries for large-scale energy storage in may types of electrical systems. For example, implementations of rechargeable multi-cell batteries can use a fixed configuration to connect multiple cells or modules in series and parallel during operation of the electrical system in order to provide the system with the required voltage and current. The use of a fixed configuration for the cells of the battery may result in low reliability and fault tolerance during abnormal operating conditions of the battery, such as high temperature, overcharge, over-discharge, or over-current. When using a fixed configuration, failure of any single cell or module in the multi-cell battery during operation of the electrical system may result in the cutoff or failure of the entire multi-cell battery. In another example, the use of a fixed configuration may not provide for efficient utilization of cell state variations, which can result in less than optimal energy conversion by the multi-cell battery. In another example, the use of a fixed configuration may not allow for flexible dynamic power management, which can result in less than optimal performance of the electrical system using the battery.
In some implementations, an electrical system that uses a rechargeable multi-cell battery can include one or more safety circuits. The safety circuits can monitor the temperature, voltage, and current of each battery cell, identifying faulty or abnormal cells in the multi-cell battery, resulting in the protection of the battery from high temperature, overcharge, over-discharge, over-current, and the failure of any of the battery's cells or modules. The safety circuits can protect battery cells from operating under abnormal conditions. The safety circuits, however, will disconnect the entire rechargeable multi-cell battery from the electrical system when any single cell in the battery operates in any one of the abnormal conditions, as the safety circuit cannot provide an effective reconfiguration topology for the multi-cell battery that would make use of the remaining functional battery cells.
In some implementations, an electrical system that uses a rechargeable multi-cell battery can include one or more cell balancing circuits. Because cell unbalance or state variations in a multi-cell battery can occur, in the fixed-configuration multi-cell battery only a part of the total capacity of the multi-cell battery can be utilized, resulting in a reduction in the useable capacity, and operating time and lifespan of the multi-cell battery. For example, as a solution to cell state variations in a multi-cell battery, cell balancing circuits can use electronic converters to transfer charge from one battery cell to another battery cell during the operation of the battery in the electrical system effectively balancing the state of charge (SOC) of the battery cells in the cell string. Cell balancing circuits transfer charges between adjacent battery cells using small currents, which can lead to slow and less than optimal battery cell balancing in the multi-cell battery. In addition, cell balancing circuits may use dissipative resistors resulting in system energy loss, may increase the cost and volume of a battery system due to the need for additional circuitry, and may only be used with multi-cell batteries where the multiple battery cells are connected in series.
In many cases, cell balancing circuits cannot provide the needed reconfiguration of the battery cells in a multi-cell rechargeable battery pack when faulty cells are detected. In some implementations, reconfigurable multi-cell battery topologies can include complex cell switching circuits that provide the power management needed for a rechargeable multi-cell battery in an electrical system. These reconfigurable multi-cell battery topologies may be too complex for battery systems that include a large number of battery cells due to the high complexity of the cell switching circuits.